<p>LECTURE 15 <a href="/tags/Reflection_(physics)/" rel="tag">REFLECTION</a> & <a href="/tags/Refraction/" rel="tag">REFRACTION</a></p><p>Instructor: Kazumi Tolich Lecture 15</p><p>2</p><p>¨ 18.1 The <a href="/tags/Ray_(optics)/" rel="tag">ray</a> model of <a href="/tags/Light/" rel="tag">light</a> ¤ Source of light rays ¤ Ray diagrams ¤ Seeing objects ¤ Shadows</p><p>¨ 18.2 Reflection ¤ Diffuse reflection ¤ The plane <a href="/tags/Mirror/" rel="tag">mirror</a></p><p>¨ 18.3 Refraction ¤ Examples of refraction ¤ Total internal reflection ¤ Fiber <a href="/tags/Optics/" rel="tag">optics</a> 18.1 The ray model of light</p><p>¨ A light ray is a line in the direction along the light energy flow. ¤ Light rays travel in straight lines forever unless it interacts with matter. ¤ Light rays can cross without interacting with each other. ¤ Each point of an object is a source of light rays. ¤ The eye sees by focusing a bundle of rays. 18.1 Sources of light rays</p><p>¨ Self-luminous objects (or sources) directly create light rays. ¤ A ray source emits a single ray. ¤ A point source emits light rays in all direction. ¤ An extended source emits light from an extended surface. ¤ A parallel-ray source produces a bundle of parallel rays. </p><p>¨ Reflective objects reflect rays originating from self-luminous objects. 18.1 Ray diagrams</p><p>¨ A ray diagram is a diagram that shows a few light rays in order to simplify the situation. 18.1 Seeing objects / Demo</p><p>¨ In order for our eye to see an object, rays from that object must enter the eye.</p><p>¨ Diffuse reflection is the process of reflecting incident light in all directions. </p><p>¨ <a href="/tags/Scattering/" rel="tag">Scattering</a> is a process in which single rays are broken into many weaker rays that leave in all directions.</p><p>¨ Demo: <a href="/tags/Laser/" rel="tag">Laser</a> and chalk dust 18.1 Shadows</p><p>¨ An opaque object can intercept rays, creating a shadow behind it.</p><p>¨ A point source creates a completely dark shadow with a sharp edge.</p><p>¨ An extended source often creates a true shadow that no light reaches, surrounded by a fuzzy region of increasing brightness. 18.2 Reflection </p><p>8</p><p>¨ <a href="/tags/Specular_reflection/" rel="tag">Specular reflection</a> is the reflection from a smooth surface.</p><p>¨ The incident and reflected rays and the normal lie on the same plane, and the law of reflection states:</p><p>�� = �� 18.2 Diffuse reflection</p><p>9</p><p>¨ Reflection from a rough surface is diffuse reflection.</p><p>¨ Light reflected off a dry street is a diffuse reflection, but light reflected off a wet street becomes more specular, and it makes difficult to see what is on the road. 18.2 The plane <a href="/tags/Mirror/" rel="tag">mirrors</a></p><p>10</p><p>¨ A plane mirror is a flat mirror.</p><p>¨ The virtual image of P is at Point P¢. � ¨ The image distance � is equal to the object distance �:</p><p>�� = � Quiz: 18.2-1 & 18.2-2</p><p>11 18.3 Refraction</p><p>12</p><p>¨ Refraction is a change in direction of light as it transmits from one medium to another.</p><p>¨ Light travels from one point to another along the path that takes least time.</p><p>¨ Angle of refraction is the angle of transmitted ray, ��. ¨ The angles of incidence and refraction, and indices of refraction of two media are related by Snell’s Law:</p><p>�� sin �� = �� sin ��</p><p>Lifeguard analog Quiz: 18.3-1 Total internal reflection / Demo</p><p>14</p><p>¨ If �� < ��, total internal reflection (TIR) occurs when the incident angle is greater than the critical angle, ��, and no refracted ray exists. </p><p>�� sin �� = ��</p><p>¨ Demo: TIR Quiz: 18.3-2 & 18.3-3</p>